I want to replace a series of numbers with that set modified

[DK]

an example would be:

438 blah blah blah
834 yada yada yada

and I want it to be
R438 blah blah blah
R834 yada yada yada

 

[DeanH]

Several ways to Find Replace these numbers as described.
Without Wildcards check box selected:
Find ^#^#^# (if the numbers are all 3 digits)
Replace R^&

With Wildcards check box selected:
Find [0-9]{3,} (if numbers are 3 and more digits)
Replace R^&

The Wildcard check box is found under the More button.

Hope this helps.
DeanH